鉄カルコゲナイドFeSe_0.5Te_0.5 超伝導薄膜へのイオン照射効果

 ―低エネルギープロトン照射によって形成された結晶欠陥と超伝導特性―

抄録

The critical temperature T_c and critical current density J_c determine the limits to practical application of superconductors. The superconducting state emerges at T_c from the formation of the Cooper pairs and macroscopic spatial coherence. The current-carrying capability, measured in J_c, is the ability of defects in superconducting materials to pin the magnetic vortices by suppressing the pair potential locally, and this may drive down the T_c of superconducting materials with short coherence length. It is a very difficult and challenging task to raise T_c and J_c simultaneously by introducing defects in the cuprate and iron-based superconducting materials. Here, we review our contribution to understanding the irradiation defect structures in iron-chalcogenide FeSe_0.5Te_0.5 (FST) superconducting thin films and their correlation to superconducting properties. Using low-energy proton irradiation, we create cascade defects in FST thin films. T_c is enhanced due to the nanoscale compressive strain and proximity effect, while J_c is nearly doubled under a zero field at 4.2 K through strong vortex-pinning by the cascade defects and surrounding nanoscale strain. This route opens up the possibility of engineering the pinning landscape for all superconductors.